Fix suffix parsing for staging releases

[olirice]

Currently, running ami-release-nix.yml on staging image with a suffix fails to parse with

copying path '/nix/store/w18zywvzwvsf5gyvs0hbbv3vlpq9zn6k-python3.12-yq-3.4.3' from 'https://cache.nixos.org/'...
jq: error: syntax error, unexpected LITERAL (Unix shell quoting issues?) at <top-level>, line 1:
.postgres_release["postgres"15""]                            
jq: 1 compile error
yq: Error running jq: BrokenPipeError: [Errno 32] Broken pipe.
Version must include non-numeric characters if built manually.

ref

this PR fixes the parsing issue